The waiting period after an embryo transfer can feel excruciatingly long. For some, distraction is key, while others like to be able to visualize what might be happening with that little embryo. Here, we break down the process of embryo implantation day by day.
What are the stages of embryo development?
Embryo development begins with the successful fusion of sperm and egg; it’s an umbrella term for the developing cluster of cells that, in pregnancy, eventually becomes a fetus. But there are several stages of embryo development that happen before that:
- Day 1: Zygote: the fertilized egg
- Day 2-3: Two-cell to eight-cell stage: the embryo after its first few cell divisions, also called cleavage stage
- Day 4: Morula: the embryo that now has about 10 to 30 cells that continue to divide—its name comes from the fact that it looks like a mulberry
- Day 5-7: Blastocyst: the mass of cells that now has two defined layers: the trophectoderm (outer cells that eventually become the placenta) and the inner cell mass (inner cells that eventually become a baby)
Often, embryos are at the blastocyst stage when they are transferred to the uterus during IVF (either in a fresh or frozen embryo transfer cycle). But sometimes, in a fresh embryo transfer cycle, the most developed embryo on the day of transfer is not yet a blastocyst, so a morulae-stage embryo is transferred with the hopes that it continues its development inside the uterus.
An embryo must develop through from cleavage stage, to morula and on to a blastocyst, when an embryo implants in the uterine lining (endometrium). So even if a day-3 embryo is transferred, it must go through these developmental stages within the uterus before implanting.
What are the steps of implantation?
Implantation is a multi-step process where the blastocyst embryo (it’ll first break out of its shell, called the zona pellucida) attaches itself to the wall of the uterus. There are three key steps that scientists have identified as part of implantation:
- Apposition: when the blastocyst lands near the uterine wall and forms an initial, very loose connection—think of this as the embryo hovering over the site of implantation.
- Adhesion: when the attachment between the embryo and endometrium occurs.
- Invasion: when the blastocyst’s outer cells penetrate the uterine wall.
These implantation steps happen over two to three days after the embryo has hatched. It’s only once they are complete that the pregnancy hormone (hCG), which is released by the embryo and can be detected in the maternal blood stream, then gets filtered through the kidneys and can be detected in the urine by an at-home urine pregnancy test.
What happens after an embryo transfer, day by day?
Whether your doctor transfers a fresh or frozen embryo, the process that follows is the same. The differences come from whether your doctor transfers a pre-blastocyst (you’ll likely hear the term “cleavage stage’ or “day-3 embryo,” which means it developed for three days after fertilization) or a blastocyst, which can be a day-5, day-6 or day-7 embryo.
What happens after a blastocyst day-5/6/7 embryo transfer
- Day 0: Embryo transfer: The embryo is transferred to the uterus.
- Day 1-2: Embryo evolution: The embryo hatches (if it wasn’t already) and continues to divide and expand.
- Day 3-5: Apposition, adhesion and invasion: The embryo makes contact with the endometrium, connects to it and implants.
- Day 6+: Cell division and hCG production: Cells that will become the fetus and placenta continue to divide, and the pregnancy hormone (hCG enters the bloodstream.)
- Day 7: Pregnancy test: hCG levels may be high enough to detect pregnancy with a urine or blood test. (Your clinic will typically wait a little longer to schedule a blood test for most accurate results.)
What happens after a cleavage stage day-3 embryo transfer
- Day 0: Embryo transfer: The day-3 embryo is transferred to the uterus.
- Day 1: Embryo development: The embryo develops into an early morula.
- Day 2-3: Embryo development: The morula develops into a blastocyst.
- Day 4: Embryo evolution: The blastocyst hatches (if it wasn’t already) and continues to divide and expand.
- Day 5-7: Apposition, adhesion and invasion: The embryo makes contact with the endometrium, connects to it and implants.
- Day 8+: Cell division and hCG production: Cells that will become the fetus and placenta continue to divide, and the pregnancy hormone (hCG) enters the bloodstream.
- Day 9: Pregnancy test: hCG levels may be high enough to detect pregnancy with a urine or blood test. (Your clinic may wait a little longer to schedule a blood test for most accurate results.)
How soon after an embryo transfer can you take a pregnancy test?
So how long does the waiting period need to be? It depends on a few factors. Typically, your clinic will schedule a pregnancy blood test (A.K.A. beta test) about nine to 13 days after your transfer.
But what if you want to try with an at-home pregnancy test? An early results test (like our lab-tested strips!) can detect very low levels of hCG, but if your doctor used a trigger shot in your pre-transfer protocol, it could have contained hCG, which a test could pick up if taken before the trigger’s hCG leaves your system. In that case, you may want to wait 14 days post-trigger, or until your blood test. Another option: some in the TTC (trying to conceive) community like to “test out” the trigger shot, where they take daily tests to watch the hCG from the trigger fade away and then look for the line to darken to indicate pregnancy.
If a trigger shot isn’t a factor, how soon you can test can be influenced by whether it was a blastocyst that was transferred or a pre-blastocyst (cleavage stage)—plus, there’s also variation in the rates of development from person to person and transfer to transfer. But generally, after a day-5, day-6 or day-7 embryo transfer, you could try testing seven days after your transfer. If you get a negative, you could try testing again two days later. If you transferred a day-3 embryo, it might take a couple days longer for hCG levels to be detectable on a test.
Feature Image from Future Fertility.